drm/amdgpu: reduce RLC safe mode request for gfx clock gating

drm/amdgpu: reduce RLC safe mode request for gfx clock gating

The driver can only request one time for the power safe mode instead of
polling and disabling the power feature each time prior to program the
GFX clock gating control registers. This update will reduce the latency
on the GFX clock gating entry.

Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>